class_docstr: A mock model of model class for TcavTest class.
    
code: def get_gradient(self, act, class_id, bottleneck, example):
      return act
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from tcav.activation_generator import ActivationGeneratorBase
  from tcav.cav import CAV
  from tcav.tcav import TCAV
  from tensorflow.python.platform import googletest
  import numpy
  import tensorflow
label_desc: Use image node_id 2 for calling the TcavTest_model obj's underlying member method code with example usage: obj.get_gradient(act, class_id, bottleneck, example) and returns: act